Catalytic cracking feed stock preparation



Sept. 13, 1960 5. J. OERTLING 2,952,632

CATALYTIC CRACKING FEED STOCK PREPARATION Filed June 16, 1958 TO VACUUM SOURCE l2 l3 1' I7 53 52 IO ZZZ-:53 23 REDUCED 25 BOTTOMS CRUDE 7 FIG. I

TO VACUUM 7 1 90 SOURCE 6| FIG. 2

REDUCED CRUDE INVENTOR:

SEWALL J. OERTLING HIS ATTORNEY United States P i CATALYTIC CRACKING FEED STOCK PREPARATION Sewall J. Oertling, New Orleans, La., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed June 16, 1958, Ser. No. 742,219. 5 Claims. (Cl. 208-361) This invention relates to the separation and recovery of a flashed distillate suitable as a feed stock for catalytic cracking from a petroleum residue. by vacuum flashing.

' The quantity of petroleum products produced by. catalytic cracking has greatly increased over the years, and to satisfy the increasing demand, various stocks, some of which were formerly considered unacceptable, have been employed as feed to the cracking units. Petroleum residue stocks have become widely used for this purpose, and in order to reduce their pitch content (a cause of catalyst fouling) various. processes have. been used, among which are propane deasphalting, delayed coking and vacuum flashing.

In the latter process the petroleum residue is heated in a furnace to achieve partial vaporization and the mixture of vapor and unvaporized liquid (pitch) is passed to a flash tower maintained under vacuum. Here the overhead vapor removed from the tower condenses to give a flashed distillate product. The process is relatively straight forward providing the catalytic cracking feed stock demand can be fulfilled with a shallow flash. Difficulties arise, however, where a deep flash is resorted to to increase the quantity of the catalytic cracking feed stock since the danger of a too high carry over of the pitch then becomes imminent. Even quite small amounts of the pitch residue entrained in the flashed vapors will severely degrade the quality of the flashed distillate as a catalytic cracking feed stock.

To lessen the pitch carry over, the partially vaporized petroleum residue stream from the furnace is commonly admitted to a centrifugal separation zone and'there most of the pitch readily separates to provide a relatively clean superheated vapor. However, because of the low pitch specification of a good catalytic cracking feed stock, it has been found necessary generally to reduce still further the pitch content of the vapor from the centrifugal separation zone. This further reduction of pitch content may be accomplished by passage of the vapor through a de-entraining zone provided with suitable'baflling, such as a foraminous mist coalescer or grid trays or both which serves to knock out most of the remaining'pitch. But in such an operation, it has developed that the baflling I must be maintained wet'inorder to, prevent a build up of the pitch which would otherwise in time cause clogging. Conventionally, this has been achieved by refluxing a sizeable portion of the flashed distillate product to the de-entraining zone where it wets the bafliing, continuously washing the mist coalescer or other baifling free of the heavy pitch material collecting thereon. The difliculty that has been encountered in wetting the foraminous mist coalescer type baffling has been described in Hausch, U.S. 2 ,809,923. There it is pointed out that in order to wet satisfactorily the coalescer that it proved desirable to dispose the reflux spray up stream of the mat within the de-entraining zone. Placement of the reflux spray immediately down stream of the mat was found inadequate as evidenced by the clogging of the mat in time. It appears that the rising vapor-from' the 5 for the wash purpose.

2,952,632 Patented Sept. 13, 19 60 underlying centrifugal separation zone is under nonequilibrium conditions and possesses a significant superheat. This excessive heat, it is theorized, vaporizes a large portion of the reflux stream making it unavailable It is thought, therefore, the placement of the Hausch reflux spray up stream of the coalescer mat assures wetting of the mat since the spray in this position can first dissipate a significant portion of the superheat before the vapor contacts the we-tted mat. With this superheat dissipation, there is less likely tO QC cur -a distilling of the liquid in the mat; thus, permitting the mat to remain wet, afiording the fluid, coalesced material collecting on the mat an opportunity to drain therefrom, avoiding clogging. It appears that the reflux distillate serves principally in two roles, namely, to dis s'ipate superheat and to wet the surface of the baflling.

' The total quantity of refluxed flashed distillate required can place a considerable burden on the condensing sys-: tem and the furnace, particularly where the throughput of a vacuum flasher is increased beyond design.

It is an object of this invention to provide anirnproved process permitting an. increase in throughput of an exist ing vacuum flasher bottlenecked by either the low reflux make capacity of its condensing system or possibly by its limited furnace design. I It is still another object of this invention to provide a process for the vacuum flashing of a residual feed stock requiring a. system having a lower furnace capacity and condensing capacity than formerly possible for the same throughput. f Another object of this invention is to provide a more economical vacuum flashing process and a process wi th reduced incipient cracking. These and other objects will become more apparent with a reading of the following detailed description of the invention when taken in con{ junction with the drawings wherein: j Fig. I is a schematic representation of a presently pro-1 ferred system for the practice of the process; and

Fig. 11 is a flow diagram of another embodiment of the process of the invention. l f It has now been discovered that in a vacuum flash-f ing process of the type employing a centrifugal separation zone (cyclone) to separate unvaporized pitch from vapor and wherein superheat'vapor from the centrifugal zone passes through a de-entraining zone provided with suitable deentrainment baffling which is maintained wet by a reflux liquid, that the amount of reflux prepared from the condensate of the vapor may be decreased by employ ing 'for a portion of the reflux, a pitch containing petroe leum residue which is introduced as a spray into the deentrainment zone up stream of the mentioned baifling: Preferably and conveniently, the. pitch containing petro; leum residue spray and the petroleum residue serving as feed to, the vaporizing furnace are of the. same composition. Surprisingly, ,the use of this pitch containing material substituted in part for the condensate reflux does not, objectionably increase the pitch content of the overhead product from the de-entraining zone. It is believed that the pitch containing residue petroleum spray dissipates or extracts a significant portion of the superheat of the vapor rising from the underlying cyclone and thus, is able to effectively replace a portion of the normal condensate reflux thereby reducing the expense of condensation, and at the same time achieving a reduction in fuel costs to the extent of the petroleum residue by-passing the furnace. The superheat vaporizes a large portion of the non-pitch content of spray, leaving its pitch content in a liquid into contact with the deentrainment bafiing. In order 3 to reduce the pitch load collecting on the bafiling, it may be desirable to employ a rather coarse spray to increase the amount of pitch falling directly to the cyclone bottom. 1 Large size spray particles also further the removal of the pitch out of the rising vapors by direct washing. Another advantage attending the process is the-reduction in the amount of incipient cracking over that normally experiencedin vacuum flashing. This adiantage will be proportional toth'e relative magnitudes of the furnace feed per se and the stream of petrolem residue by-passing the furnace.

i In the preferred arrangement as illustrated in Fig. 1 and described in the example below, the lower spray (preferably a portion of the feed) is sprayeddownwardly into the rising vapors from the centrifugal separation ione, with no grid tray or mist coalescer placed below it.v 'The upper spray which is supplied with a product distillate (condensate) reflux is spaced above this lower spray with one or perhaps more grid trays interposed therebetween and preferably immediately below a fram-- {nous mist coalescer. .The grid tray and the coalescer are maintained in a wet condition to avoid clogging. It is believed that the lower spray dissipates a significant portion of the superheat of the rising-vapor before it con- {acts the wetted bafiiing- By this arrangement, it will be seenthat the amount of reflux distillate or condensate required isreduced to the e'xtent'that the feed reflux (the lower spray) dissipates superheat. The'feed reflux, should not be substituted completely for the condensate reflux because the pitch content of the overhead vapor stream-can then be expected tobecome objectionably large. Preferably, the lower reflux spray of the pitch containing petroleum residue is used in an amount .that will dissipate at least a significant portion ofthe'superheatv of the vapor before it contacts the de-entrainment surface, but in an amount that will not increase the pitch content of the vapor stream beyond the normally tolerated 4 V baffling in a wet condition which assures that the pitch collecting thereon will continuously drop off, falling to the bottom of the de-entraining zone from whence it is removed. In the practice of this embodiment it is recommended that a large size particle spray may be employed for the lower spray.

Conceivably, the lower feed spray may be placed between, say the, bottom two of the grid trays in the instances where multiple trays are utilized between the two sprays. However, if this is done, it is essential that the vapor flow be uniformly distributed over the cross section of the de-entraining zone before contacting the lowermost grid tray. Otherwise, there will be a liquid build up and a dumping of the liquid on the lowermost tray, resulting in a wide variation in pressure drop across that tray and a surging of the bottoms level. To lessen the likelihood of this occurrence, in the preferred embodiment of Figure 1, thespray is placed below the single tray. Normally, only a single tray need be employed betweenthe two sprays.

With reference to Fig.1 a reduced crude stream flowi-ng through, a line .10 enters a furnace '11 where the reduced crude is heated to a conventional elevated temperature in the range of- 775-825 F. to vaporize substantially all of the stream, excepting the heavy pitch portion. The vaporized stream moves through a transfer line 12 to a tangential inlet of a cyclone separator 13 whichforms the lower portion of an integrated vacuum flasher 15. The vacuum flasher is generallyof a conventional design' with the centrifugal separation zone containing a centrally disposed stand pipe 17 within the cyclone; The swirling vapor stream being blocked from passing upwardly by a collar 19 which encompasses the in .an acceptable catalytic cracking feed stock. Generally speaking, 0.5 to 1.0 volumes (barrels) of the lower reflux are employed for a volume of the upper reflux. It is normal practice in conventionalvacuum.flashing systems and in the process of the invention, to use in the range of 0.07 to 0.12 barrel of reflux (the two sprays combined inthe instance of invention) per barrel of the petroleum residue throughout. 7 V

Petroleum residues generally of the type employed for thepreparation of a catalytic cracking feed stock are suitable both as furnace feed and as residue spray to the d'e-train'ing zone. Both short and long residues ofvarying. pitch content may be employed.

The conditions of temperature and subatmospheric pressure used in the process of the invention are substantially those conventionally employed for vacuum flashing generally. The portion of the feed diverted around the furnace for use as a lower spray to the de-entraim'ng zone is preferably introduced at a relatively low temperature to permit the greater adsorption of superheat per volume flow of the feed reflux. However, if the long residue or other residual feed is available at a higher temperature, it may be used without cooling.

' "The practice of the invention is not limited to the pie-- ferred scheme as illustrated in Fig. 1 butmay be utilized inconnection with other baflling and spray arrangement to achieve a dissipation of at least a significant portion of the vapors superheated prior to its contacting of the condensate reflux wetted portion of the baffling. 'An alternative embodiment is illustrated in Fig. '11 and there it will be seen there is no bafiling interposed between the two sprays; The lower feed spray contacts the hot, superheated vapor exiting from the underlying centrifugal separation zone, dissipating at least a 'considerablepor tion of the excess heat prior to the vapors'contacting of the foraminous'mist coalescer type bafllingwhich is placed in-that embodiment immediately abovethe condensate reflux spray. The upper spray maintains the stand pipe, passes downwardly along the outside of the stand pipe and then upwardly through the stand pipe into an overlying 'de-entraining zone 21. The upper, open endof the stand pipe has a deflector 14 spaced immediatelyabove it. The inverted show oif device 16 (around the top of the stand pipe) is designed to direct any pitch that maybev crawling upwardly of the interior wall of the stand "pipe into the annular removal trough defined by .the col1ar'19. Most of the liquid pitch carried by the vapor stream drops out and collects in the bottom reservoir 23 of the cyclone separator. The material collecting there is removedthrough an exit line 25. In Fig. 1, the rising vapors first encounters a spray of the pitch containing feed from nozzle 27. The nozzle is supplied witha portion of the feed diverted around the furnace via'a line 29 which in turn connects into the feed supplyline 10. Immediately downstream'of the feed spray nozzle, there is placed a single grid type tray 22 of conventional design. The tray is maintained wet and assists inreducing the pitch content of the vapor stream passing through the de-entraining zone. Above the grid tray there .is disposed within the de-entraining zone a second set of spray nozzles 28. This set of nozzles, similar to the one below, is conventional in design and is the Schuyler mat.

stantially all of the rising vapors are covered by the spray. Thev liquid for the nozzles of this top spray is supplied viaa line 31 which connects to the liquid outlet of a vapor-liquid separator 33 through la line 35.

l 7 There is placed in the upper portion of the de-entraining zone immediately above the upper spray a foraminous mist-coalescer 30 of conventional design. A preferred coalescer takestheform of a mat of tangle wire several inches thick, such as, for example, the York mat manufactured by Otto York, Inc., West Orange, New Jersey, or the Metex mat "manufactured by the Metal Textile Corporation, Roselle, New Jersey. These mats have an openvolume upwards of% and a density between 3-15 pounds per cubic foot depending on the degree of wire compression. -Another suitable coalescer. is

Such mats present a very'small presl116; d1'Qp.; t i V The coalescer mat 30 substantially completes the removal of the pitch entrained in the rising vapor and the vapor passes therethrough into the head space of the deentraining zone, leaving through a removal line 37 which opens into a partial condenser 39, cooled by water, where the heavier components of the vapor stream are condensed. The vapor stream in an alternative may be cooled by the feed prior to its passage to the furnace 11. The remaining vapor and condensate flow to the separator 33 and there the condensate (heavy flashed distillate) collects in the bottom of the vessel and is removed through the previously mentioned line 35. A portion of the heavy flashed distillate is returned as refluxvia line 31 and the remainder is transferred in a line 41 to catalytic cracking.

The vapors collecting in the head space of the separator 33 leavethrough a line 43 to a second condenser 45 where the rest of the petroleum residue vapors are condensed and subsequently separated in a vessel 47. The

light condensate is removed from this latter vesselrvia a line 49 and may be transferred to the catalytic cracking unit or other usage. A vacuum source is connected to this latter separation vessel 47 via a line 50.

' The pitch dropping from the de-entraining baifling collects in the annular removal trough (which has at its bottom the collar 19) of the de-entraining zone. From there ,the fluid pitch flows through a run back line 52 to the pitch reservoir 23 placed below the cyclone.

In Fig. 2 the reduced crude enters a furnace 60 via a line 61. The vaporized reduced crude exits from the furnace through a transfer line 61 and is introduced to a' cyclone 64 below a vacuum distillation unit 65. The entrained pitch drops out of the swirling vapor and falls to the top tray of a steam stripping tower 66, disposed directly beneath the cyclone separator. vapor of low pitch content leaves the cyclone through its centrally dis'posed stand pipe 67, passing upwardly into the overlying de-entraining zone 69 of the vacuum flasher. Here the vapor is first contacted by a spray of the feed from a first nozzle arrangement 71. The set of nozzles is "in the lower portion of the de-entraining zone spaced some distance up stream of a second set 73 of similar nozzles. Preferably, the lower nozzles are designed to provide a spray with larger drop size than the upper spray. The feed for the lower spray 71 is supplied by a line 75 which branches off of the reduced crude feed line 61, a short distance preceding the furnace. The lower spray extracts much of the superheat of the rising vapor which continues upwardly through the de-entraining zone into contact with the aforementioned second spray. The second spray is a heavy flashed distillate (condensate) which is recovered from the vapor product leaving the de-entraining Zone. The second spray wets a coalescer mat 77 which is placed immediately above the second nozzle set 73. The vapor leaves the vacuum flasher through a line 79 into a partial condenser 80 where the heavy flashed distillate condenses and is subsequently separated from the remaining vapor in a separating vessel 83. The heavy flashed distillate is removed from the latter vessel through a line 85 and returned in part through a line 87 as the reflux to the upper spray nozzles 73., The rest of the heavy flashed distillate condensate is passed to the catalytic cracking unit in a line 89. Vapor from the separating vessel 83 leaves in a conduit 90 which opens into a second condenser 91 where the remaining petroleum vapor is condensed. The light flashed distillate is removed as a liquid through line 93 from the bottom of a separating vessel 94. The head space of this latter vessel connects through a line 95 to a vacuum source.

The pitch collecting on the coalescer mat falls to a pitch removal annular trough 96 and from there passes through a run-back line 97 into the steam distillation tower 66. Steam enters via a line 101 and a nozzle 98 into the lower portion of the distillation tower to strip the lighter material from the heavy pitch. The pitch collects Superheated to the processing of reduced crudes of relatively highpitch content and is accordingly best used in the processingof low pitch content residues and in relatively low throughputs.

r EXAMPLE Eight evaluationitests were conducted at varying transfer temperatures, amounts and types of reflux to the upper and lower sprays in a pitch de-entraining system of the; type illustrated in Fig. 1. The first three tests (runs 1-3) were conducted with varying amounts of a heavy flashed distillate to the lower and upper reflux sprays 27, 28 respectively. The heavy flashed distillate is the condensate collecting in the bottom of the separating vessel 33. These first three tests typify conventional practice. The following three tests (runs 4-6) employ varying amounts of the heavy flashed distillate refluxed to the upper reflux spray with differing amounts of a straight run residue supplied to the lower reflux spray 27. The feed to the furnace 11 is of the same composition as this lower reflux spray. The three runs 4-6 represent the processfof the invention. a

Thecon'ditions and results of the several runs are reported in the table below. In all of the first six runs the furnace transfer temperature was kept constant. The entry entitled Feed is the feed to the furnace and the H.F.D. reflux upper and H.F.D. reflux lower are the volume flows of the heavy flashed distillate, respectively, to the upper and lower sprays 28, 27 expressed in barrels perday (b./d.-). The volume of vapor passing overhead from the flasher through the line 37 appears under the item Overhead and is expressed as a total condensate ih.b./d. f In the instance of runs 4-6, the entry S.R.R.' reflux lower is a' volume account in barrels per day of the straight run residue supplied to the lower reflux spray; The Pitch entry represents the amount of pitch rfiinQved in barrels per day through the bottoms line 25. The item entitled Pitch percent (based chg.) is a percentage ratio of the pitch in the feed entering the furnace 11. The item Pitch ent. is an expression of percentage ratio by weight of the pitch entrained in the vapor stream 37. The Transfer temperature item is the temperature of the heated residual stream leaving the furnace while the Vaporline entry is the temperature of the vapor leaving the de-entraining zone in line 37. The pressure of the flasher is taken at the top of the de-entraining zone, above the coalescer mat.

Table Run No. 1 2 3 4 5 6 7 8 Feed, b./d 37, 200 37, 200 38, 682 38, 682 38, 226 36, 000 36, 000 H.F.D. Reflux Upper b./d 2, 000 1, 520 1, 520 2, 000 2, 000 2,000 2,000

Lower, b./d 1, 480 1, 480

Lower, b./d 1, 480 1, 480 1,026 1, 520 1, 520 Overhead, b./d 25, 643 25, 897 27, 252 27, 27,050 25, 713 26, 348 Pitch 11, 557 11,303 11, 430 11, 557 11,176 10, 287 652 Pitch percent (Based Chg)- 30. 73 31. 07 30. 38 29. 55 29. 88 29. 24 28. 58 26. 81 Pitch Ent., percent w 0. 15 0. 06 0.10 0. 11 0.20 0. 28 Transfer Temp.

F 776 776 776 776 776 776 790 802 Vaporline, F. 720 718 726 729 723 726 732 74.2 Flasher Top:

Press, mm. Hg- 129 130 130 128 128 130 120 124 The runs within the following pairs are best compared, namely, runs 3 and 4, runs 2 and 5 and runs 1 and 6. It will be seen that the individual runs of the foregoing pairs have the same volume flows to their respective assaesa a ed, di t e w ss r c as h lo sr' sp The several tests and control runs have the same order of pitch entrainment, indicating there was .no appreciable change in the flashed distillate quality as measured by pitch entrainment. There is a significant increased throughput for the test runs 4-6 at the same 'furnace transfer'temperature. Run 6 gave the lowest overallpitch production while using 2000 b./d. of the heavy flashed distillate to the upperspray and 1000 b./d. of straight run residue to the lower spray. Runs 7 and 8 were conducted to determine the effect of increased furnace temperature on pitch yields. It ;will 'be seen that at the highertransfer temperature there is a reductionof 1;.7 7,% in pitch production.

I claim as my invention: p

I. In a vacuum flas ing process 'for the-preparation of a'catalytic cracking feed stock of'an acceptable low pitch content from a pitch-containing petroleum residue, .wherein the process involves heating the residue in a furnace to, provide an unvaporized pitch entrained in a vapor, passing the vapor through a centrifugal separation zone and there separating superheated vapor from most of the pitch, subsequently removing the superheated vapor to a dei-entraining zone and there passing the vapor upwardly through the zone'into contact witha de-entrainment surface disposed vtherein and wetted by a reflux. liquid constituting a .part 'of the product condensate'of the vapor leaving said de-entrainment zone to lowerstill further the pitchcontent of the vapor by retention of pitch on said tie-entrainment surface, the improvement comprising contacting the vapor upstream of thewetted de-entrainment surface and beyond the centrifugal separation zone with a pitch containing petroleum residue spray introduced in an amount effective to dissipate at least a significantportion of the superheat of theivapor before it contacts said de-' entrainment surface, thus reducing the amount of the product vapor condensate refluxed to the deentraining zone, and permitting a reduction in furnace fuel cost.

'2. A process insac'corda'ncewith claimluwherein the pitch containing petroleum residue spray and the petrol'eum residue to the furnace are of the samecomposition. "3. In a vacuum flashing process for the vpreparation of a catalytic cracking feed stock trom a petroleum residue,

wherein the process involves heating the residue ina furnace to provide an unvaporized pitch entrainedin a vapor, passing the vapor to a centrifugal separation zone' and there separating superheatedvapor from most of the pitch, subsequently removed the superheatedva'por' to a deentraining zone and there passing the vapor upwardly through the zone into contact withra ,de-entrainment 'sur- 7 face disposed therein and wetted by a reflux liquid prepared from the product vaporrcondensate leaving said deentraining zone to lower still further the pitch content of the vapor by retentionof pitch on said tie-entrainment surface, the-improvement comprising spraying the super heated vapor from the centrifugal separation zone with a relatively low temperature, pitch-containing petroleum residue within the de-entraining zone upstream of said de-- entrainment surface to dissipate a substantialportion of the super-heat before the vapor contacts said de-entraim ment surface, said de-entrainment surface comprising a foraminous mist coalescer which is wetted by a spray of the product reflux introduced to the de-entraining zone immediately upstream of the coalescer and beyond the place 'of spraying of the pitch-containing petroleum .residue, thus reducing the amount of the product vapor condensate refluxed to the de-entraining zone and permitting 7 a reduction in'furnace fuel cost.

I 4.;A process in accordance with claim 3 wherein the pitch-containing petroleum residue spray and the petroleum residue to the furnace are of the same composition, and about one volume of the petroleum residue spray is employed for a volume'of the vapor reflux spray.

5; A ,process'in accordance with claim 3 wherein the d e-entrainment surface comprises in addition to the toraminous coalescer,at least one grid plate maintained in a; wetted condition and placed between the two sprays to assist in the displacement or the pitch from the vapor.

References Cited in thefile of this patent UNITED STATES PATENTS 1,924,163 Miller Aug. 29, 1933' 1,774,723 Moyer Dec. 18, 1956- 2,809,923 Hausch Oct. 15, 1957 Cavin .a Sept. 10, 1957 

1. IN A VACUUM FLASHING PROCESS FOR THE PREPARATION OF A CATALYTIC CRACKING FEED STOCK OF AN ACCEPTABLE LOW PITCH CONTENT FROM A PITCH-CONTAINING PETROLEUM RESIDUE, WHEREIN THE PROCESS INVOLVES HEATING THE RESIDUE IN A FURNACE TO PROVIDE AN UNVAPORIZED PITCH ENTRAINED IN A VAPOR, PASSING THE VAPOR THROUGH A CENTRIFUGAL SEPARATION ZONE AND THERE SEPARATING SUPERHEATED VAPOR FROM MOST OF THE PITCH, SUBSEQUENTLY REMOVING THE SUPERHEATED VAPOR TO A DE-ENTRAINING ZONE AND THERE PASSING THE VAPOR UPWARDLY THROUGH THE ZONE INTO CONTACT WITH A DE-ENTRAINMENT SURFACE DISPOSED THEREIN AND WETTED BY A REFLUX LIQUID CONSTITUTING A PART OF THE PRODUCT CONDENSATE OF THE VAPOR LEAVING SAID DE-ENTRAINMENT ZONE TO LOWER STILL FURTHER THE PITCH CONTENT OF THE VAPOR BY RETENTION OF PITCH ON SAID DE-ENTRAINMENT SURFACE, THE IMPROVEMENT COMPRISING CONTACTING THE VAPOR UPSTREAM OF WETTED DE-ENTRAINMENT SURFACE AND BEYOND THE CENTRIFUGAL SEPARATION ZONE WITH A PITCH CONTAINING PETROLEUM RESIDUE SPRAY INTRODUCED IN AN AMOUNT EFFECTIVE TO DISSIPATE AT LEAST A SIGNIFICANT PORTION OF THE SUPERHEAT OF THE VAPOR BEFORE IT CONTACTS SAID DEENTRAINMENT SURFACE, THUS REDUCING THE AMOUNT OF THE PRODUCT VAPOR CONDENSATE REFLUXED TO THE DE-ENTRAINING ZONE AND PERMITTING A REDUCTION IN FURNACE FUEL COST. 